With the recent development of study on enhancement of immune response aiming at antitumor effect, further detailed studies on immunological antitumor activities have been conducted.
Enhancement of immune response includes enhancements of humoral immunity, cell-medicated immunity, macrophage function, etc. With respect to cell-mediated immunity, an attempt to enhance effector T cells (hereinafter referred to as "T.sub.E cells") has been investigated.
T.sub.E cells receive a great deal of attention since they, when induced in a living organism, react specifically with tumor cells produced in the living organism to destroy the tumor cells.
The present inventors considered the mechanism of T.sub.E cells generation in a living organism as summarized in what follows.
In case normal cells are transformed into tumor cells, "tumor associated antigens" appear in the tumor cells. On the other hand, when tumor-bearing hosts are immunized with hapten-modified autologous cells, hapten-reactive helper T cells are induced. In this condition, if the tumor surface is modified with hapten, the preinduced hapten-reactive helper T cells can enhance generation of T.sub.E cells specific to the tumor cells. The T.sub.E cells recognize the tumor associated antigens and destroy the tumor cells.
The term "hapten" herein used means an incomplete antigen which per se lacks immunogenicity but, upon being conjugated to autologous serum proteins or autologous cell surfaces, potentially induces T cell activity in vivo.
The present inventors found 2,4,6-trinitrophenyl group (TNP) to be capable of playing a role as a hapten exhibiting immune response specific to tumor cells and proved the above-described reaction mechanism (J. Exp. Med., 149, 185-199 (1979) and J. Immunol., 124, 863-869 (1980)). However, application of the immunotherapy using TNP as hapten to tumors in human is not satisfactory in view of toxicity of TNP and the like.